Fiber glass comes in many shapes and sizes and can be used for a variety of applications. A general discussion of fiber glass technology is provided in "Fiber Glass" by J. Gilbert Mohr and William P. Rowe, Van Nostran Reinhold Co., New York 1978 which is herein incorporated by reference.
As discussed in "Fiber Glass", glass fibers are generally mass produced in two types: bulk or blown fiber for insulation and allied applications, and continuous-filament, or reinforcing fibers. In either form raw fiber glass is abrasive and easily fragmentized. Damage to the individual glass fibers can occur as a result of the self-abrasive motion of one fiber passing over or interacting with another fiber. The resulting surface defects cause reductions in overall mechanical strength.
Consequently, binders have been developed to prevent these problems. A typical binder may prevent the destructive effects of self-abrasion without inhibiting the overall flexibility of the finished glass fiber product. Extremely good resistance and resilience to conditions of elevated humidity and heat are beneficial in view of the wide variety of end use applications for glass fiber/binder compositions.
One of the most important performance properties is a consequence of the practical realities of the glass fiber manufacturing business. Cured glass fiber/binder compositions are normally very bulky and voluminous. Batts and rolls used as insulation in buildings have densities ranging from 0.5 to 1.0 pound per cubic foot (pcf) and generally require binder contents of 3 to 7% by weight. Since it is prohibitively expensive to ship such materials in an uncompressed state, the batts and rolls are bundled and compressed in packages to 8 to 25% of their manufactured thickness. During the shipping process these packages are normally subjected to conditions of elevated temperature and humidity. Once the compressed batt or roll reaches the consumer and is removed from its packaging, it should recover between 40% to 100% of its original volume. Insulation materials not achieving such recovery values normally have difficulty meeting advertised thermal resistivity (R) values. In general, the better the recovery value of the glass fiber/binder composition, the better insulating properties the composition will possess.
Fiber glass products denser than 0.7 pcf generally have load bearing requirements, either in the form of compressive or flexural strength, as well as thermal and sound attenuation restrictions.
The amount of binder present in a fiber glass product is dependent on several factors including the product shape, the type of service required, compressive strength requirements and anticipated environmental variables such as temperature. Binder content is determined by the loss on ignition test, described below, and is given as % L.O.I. In general, binder contents may range from 1 to 25% L.O.I., depending on the specific end use application. Applications include sound control batts with low binder content; industrial-grade thermal insulation for driers, ovens, boilers, furnaces, and other heat generators; low-to-intermediate L.O.I. duct liners and fiber glass flexible ducts and high-L.O.I. rigid ducts; and pipe insulation with intermediate to high binder levels. Molded fiber glass parts (e.g., automotive topliners) are generally thin pieces of high density (15-22 pounds per cubic foot at 1/8 to 3/8 inches thick, for example) and require binders to provide excellent flexural strength. Fiber glass products used for filtration have wide ranges of fiber diameter and binder levels.
Traditionally, high compressibility ratios, recovery values and other desirable properties have been obtainable only with phenol formaldehyde resins. As a result, for many years glass fiber binders have been almost exclusively based upon phenol formaldehyde resins. These systems typically include aminoplast resins such as melamine and urea, silicone compounds, soluble or emulsified oils, wetting agents, and extenders or stabilizers.
Although widespread, the use of phenol formaldehyde resins in binders for fiber glass involves numerous problems and disadvantages.
Chief among these is the difficulty in complying with ever stricter environmental regulations. Typically these phenolic binders contain large amounts of low molecular weight species including phenol, formaldehyde and volatile 1:1 and 1:2 phenol formaldehyde adducts such as 2-methylolphenol and 4-methylolphenol. During the curing process, these volatile low molecular weight components are released into the atmosphere in substantial volumes as volatile organic compounds (VOC). Since the process of manufacturing fiber glass typically involves spraying large volumes of phenol formaldehyde binders into high volume air streams, and then curing the product in convection ovens that involve high volumes of air, fiber glass manufacturers have an urgent need to reduce their VOC emissions, particularly with regard to formaldehyde.
Attempts at reducing the free formaldehyde content of typical phenol formaldehyde binders have been unsuccessful because excess formaldehyde is essential to curing and bonding in such systems. Techniques such as scrubbing and incineration would require substantial financial expenditures with the potential for uncertain results.
Attempts to convert free formaldehyde into less obnoxious and dangerous chemicals have involved the addition of ammonia or urea. Such additions were intended to convert free formaldehyde into hexamethylenetetramine or a mixture of mono and dimethylol ureas. Unfortunately however, urea, hexamethylenetetramine, and mono and dimethylol ureas can all contribute to the production of trimethylamine, which gives the cured phenolic binder and finished product an undesirable "fishy" odor. In addition, nitrogen containing compounds can decompose to yield ammonia and other potentially harmful volatile compounds.
Phenol formaldehyde resins also require careful handling procedures. Since the cooked resin must be refrigerated until use, refrigerated trucks and holding tanks are required. Even with refrigeration, the storage life of a phenolic resin is typically 15 days.
Adding to these problems is the fact that phenol formaldehyde resins have a short life span. Finished binders based on such resins must used within 2 to 12 hours of their initial formulation.
Finally, because phenol formaldehyde resins are petroleum based, they are particularly vulnerable to fluctuations in price and availability.
As a result, an alternative to phenol formaldehyde based fiber glass binders has long been sought.
The present invention solves the problems caused by the use of phenol formaldehyde resins in binders for fiber glass by providing binders based on aqueous compatible furan resins. The furan binders of the instant invention provide many of the advantages of phenolic binders while resulting in substantially reduced VOC emissions. What is particularly desirable about the furan binders disclosed herein is the use of water as a significant component.
The furan binders of the present invention have several advantages. Formaldehyde is not a significant curing or decomposition product and the furan resins form very rigid thermosets. Since furan resins are derived from vegetable cellulose, a renewable resource, they are inexpensive and readily available.
It is, therefore, an object of the present invention to provide a binder for fiber glass which will provide substantially all of the advantages of phenol formaldehyde binders while simultaneously resulting in significantly reduced emissions of volatile organic compounds, particularly formaldehyde.
Another object of the present invention is to provide methods of applying the novel furan binder to raw or bare glass fibers so as to provide the required performance characteristics.
Finally, another object of the invention is to provide glass fiber compositions employing the novel binders which are suitable for incorporation into a variety of end use applications.